When iron reacts with oxygen, it forms iron oxide, or rust.

To determine how much iron oxide (rust) is formed when iron reacts with oxygen, we can use the principle of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction.

In this case, you start with 112 g of iron and 24 g of oxygen. The total mass of the reactants will equal the mass of the product (iron oxide).

Total mass of reactants:
- Mass of iron = 112 g
- Mass of oxygen = 24 g

Total mass of reactants = 112 g + 24 g = 136 g

Since iron oxide is the only product formed from this reaction, the mass of the iron oxide formed will be equal to the total mass of the reactants.

Therefore, the mass of iron oxide formed is **136 g**.

So the correct answer is:
**B. 136 g of iron oxide**.